1. Field of the Invention
The preset invention relates to a multi-joint robot provided with at least two axes and having a function for evacuating or repositioning an arm thereof.
2. Description of the Related Art
Recently, a cooperative robot, which is operated while sharing a working area with a human, has become popular. For the safety of the human, such a cooperative robot may be configured to be stopped or suspended when the human approaches or contacts the cooperative robot.
However, since the cooperative robot shares the working area with the human, the suspended robot may interfere with the work of the human. In such a case, the robot is desired to be able to be repositioned. As a means for repositioning the robot, it may be desired for the human to be able directly push and easily move the robot without operating a teaching board, for example.
As relevant prior art documents, JP H08-071969 A discloses that a soft-floating servo control is used so that, when a strong external force is applied to a robot, a servomotor for driving a mechanical unit of the robot does not forcibly output a large torque which exceeds the external force.
Further, JP H10-291182 A discloses an arm drive unit for correctly detecting a force (or disturbance) applied to an arm by an operator, in which a magnetic torque sensor is attached between the arm and a speed reducer of a motor for driving the arm.
In JP H08-071969 A, a motor current is used to calculate the torque applied to an axis. However, in such a method, the correct torque may not be obtained, since the calculated torque may include a frictional influence. As a result, the force of the direction thereof applied by the human cannot be correctly detected.
On the other hand, as described in JP H10-291182 A, when a torque sensor is arranged on each arm, it is possible to eliminate the influence of the friction. However, it is necessary to provide the torque sensors as many as the arms (axes), which raises a cost of the robot (in particular, a multi-joint robot).